Montana-Dakota Utilities fast-tracked the construction of two internal combustion engines at its Lewis & Clark coal plant, leaving open the option to install two more engines there at a later date.
Those were among the points made in an Oct. 14 rate application from Montana-Dakota Utilities filed at the North Dakota Public Service Commission. Alan L. Welte, the Director of Generation in the power production department of Montana-Dakota Utilities, outlined several projects done recently where the company is now trying to recover project costs in rates.
Lewis & Clark Reciprocating Internal Combustion Engine (RICE) Project
The Lewis & Clark RICE Project is the addition of an 18.6-MW natural-gas fired reciprocating internal combustion engine project comprised of two 9.3-MW Wartsilla 20V34SG generating units. The RICE units have very low emissions and are equipped with a Spark Ignited Lean Burn Combustion system as well as Selective Catalytic Reduction (SCR) for NOx removal and Catalytic Oxidation (CatOX) to control CO emissions. This is a brow field project constructed adjacent to the Lewis & Clark coal-fired facility near Sidney, Montana. The RICE Project is interconnected into the existing Lewis & Clark 115-kV substation and receives natural gas through the existing WBI Energy Transmission pipeline serving the Lewis & Clark Station.
With the development of new natural gas sources and pipelines in the Bakken Area, Montana-Dakota was able to contract with WBI Energy for firm natural gas transportation at the Lewis & Clark Station which was previously unavailable. Montana-Dakota was also able to secure favorable natural gas supply rates and fuel management services for the RICE units as provided under the existing Heskett Unit 3 agreement with Tenaska Marketing Ventures.
Welte noted that the layout for the Lewis & Clark RICE Project was designed for the potential expansion of two additional 9.3-MW Wartsilla 20V34SG units in the future. Montana-Dakota scaled back the size of the Lewis & Clark RICE Project to reduce the total investment and shorten the overall project schedule.
Successful achievement of performance and emissions guarantees have been demonstrated through testing and the units are operating very well, Welte said. Through Sept. 15, the Lewis & Clark RICE Station has been operated 105 times for 683.6 hours and has produced 7,045 net MWh of energy. The total cost at this time is $47.2 million.
Scrubber modifications at Lewis & Clark to comply with EPA’s Mercury and Air Toxics Standards (MATS)
To comply with the non-mercury hazardous pollutant metals portion of the MATS Rule, Montana-Dakota installed the following additional equipment and scrubber modifications:
- Turning vanes to improve the distribution of the flue gas within the stack;
- A sieve tray and mist eliminator system to increase the efficiency of removing filterable particulate matter (FPM) which is the surrogate for the non-mercury metals;
- Replacement of scrubber slurry recycle pumps;
- A forced oxidation system to control the chemical reactions within the system and to prevent deposits from forming on the scrubber surfaces; and
- A weather enclosure was added to the stack to allow for required year round emissions testing.
The majority of the Lewis & Clark MATS project construction activities were completed during an eleven-week scheduled outage in September-November 2015. Initial operation, tuning and preliminary testing was completed from late November through mid-December 2015, and commercial operation of the new systems was achieved on Dec. 23, 2015.
Compliance with EPA final CCR Rule published in April 2015
The Lewis & Clark Ash System project was implemented as a result of the CCR Rule and can be divided into three main parts:
- retirement of the large ash pond;
- construction of a new concrete bottom ash tank; and
- modifications necessary to handle fly ash entirely as a dry material.
The large ash pond was retired since continued long-term operation of the pond would have resulted in a higher cost of compliance than other ash management options. The large ash pond was used to settle out sluiced solids including bottom and fly ash, as well as those contained in scrubber pond and water treatment blow downs, and temporarily store them prior to dewatering. After dewatering, the solids were transported to the station’s dry ash disposal site located on company-owned property, which is an abandoned surface coal mine near Savage, Montana. At the large ash pond, it discontinued sluicing operations, dewatered the pond, and filled it. With the exception of final shaping and capping scheduled for 2017, this work was completed in October 2015, during the scheduled MATS Project outage.
AQCS equipment at Big Stone coal plant to comply with the South Dakota State Implementation Plan for the EPA’s Regional Haze and MATS rules
To comply with the Regional Haze Rule, the following equipment was added:
- Selective catalytic reduction technology (SCR) with separated over-fired air for control of NOx;
- Circulating dry scrubbers for control of SO2;
- Replacement baghouses for control of particulate matter;
- Replacement of induced draft fans;
- Modifications to the boiler tube surfaces to obtain the required SCR inlet flue gas temperature and to the boiler structure to meet the new pressure requirements for the boiler setting;
- Pebble lime and ammonia reagent handling systems;
- Waste ash handling system; and
- An activated carbon injection system was installed to comply with the mercury limit of the MATS Rule.
Big Stone was shut down in February 2015 to “tie-in” the AQCS equipment. The outage was scheduled to be completed and the unit back on line by June 9, 2015, but because of problems found with the plant’s High Pressure (HP) steam turbine during routine inspection, the outage had to be extended. The plant returned to service in August 2015, following the HP steam turbine repair and blade replacements which were unrelated to the AQCS Project. Construction of the AQCS Project was completed in the third quarter of 2015. Following initial operation, tuning, and testing the AQCS was declared commercially operational on Dec. 29, 2015. Activities in 2016 centered on contract close outs, demolition of the old baghouse, and site restoration.
Coyote Station Boiler Lower Wall Replacement Project
The Boiler Lower Wall Replacement Project involved the replacement of sections of the boiler lower water wall tube panels, including the cyclone burner throat openings. Inspections had revealed that micro-tangential cracking was appearing over the entirety of the lower water wall tubes which was the likely result of heat cycles, erosion and the extremely harsh environment experienced in this area of the boiler over time.
The replacement project was needed to avoid future failures of the water tubes. It also allowed for the resizing of the cyclone throat openings to complement the installation of the advanced over-fired air system which was installed to comply with the North Dakota State Implementation Plan for the EPA Regional Haze Rule.
The project was completed during a scheduled major outage occurring from March 20 to June 10, 2016. Montana-Dakota’s ownership share of the cost is $4.6 million. In addition to preventing future tube failure outages, through the resizing of the cyclone burner entrance throats, this project contributed to the successful balancing of air flow and differential pressures in the cyclone burners and the boiler.
Limestone Project installed at Heskett Station Unit 2 to comply with the North Dakota State SIP for the EPA Regional Haze Rule
The Limestone Project included the installation of equipment necessary to unload, store, and convey limestone to the existing Unit 2 atmospheric fluidized bed combustor (AFBC) portion of the boiler. The limestone is a reagent that will be used in combination with the existing fluidized bed sand material to provide the chemical reactions required to reduce SO2 emissions.
The project construction began at the end of September 2015. Equipment was tied-in during a scheduled Unit 2 outage in March 2016, and construction was completed in early June 2016. Initial operation, tuning and preliminary testing of the equipment was completed by the end of June 2016. Testing to select the best limestone from two different suppliers and to begin optimizing its use in the AFBC to control SO2 was conducted in July 2016. In September, a demonstration test of the selected limestone began which includes further optimization and adjusting of limestone feed controls. This will be followed by the continuous use of limestone as required to meet the May 7, 2017, compliance date. The project cost is projected to be $9.7 million.